Buoyant Force

Why is the fluid's density taken in the buoyant force?
If the system is in equilibrium, then isn't the buoyant force compensating for the weight of the object? In such a case, shouldn't the density of the object be considered?

Staff: Mentor

Why is the fluid's density taken in the buoyant force?
If the system is in equilibrium, then isn't the buoyant force compensating for the weight of the object? In such a case, shouldn't the density of the object be considered?

The buoyant force is due to the net effect of the fluid pressure on the object. That depends on the density of the fluid. The density of the object is irrelevant: Replace the object with another of same shape and size but different density and the buoyant force will be the same. Of course, if the object is in equilibrium, then you know that the buoyant force must equal its weight.